After downloading the Trades Math Calculator you may get this message when you begin the installation. The explanation for this is as follows:

Microsoft has increased user security by enhancing a feature, first introduced in Internet Explorer 7, called SmartScreen Filter. SmartScreen Filter helps detect phishing websites. It can also help protect you from downloading or installing malicious software.

When you download a program from the Internet, SmartScreen Filter will check the program against a list of programs that are downloaded by a significant number of other Internet Explorer users and a list of programs that are known to be unsafe.
If the program you are downloading is not on the first list, or is listed as unsafe, SmartScreen Filter will display a warning that the file is not commonly downloaded.

Per Microsoft’s site (http://windows.microsoft.com/en-US/windows7/SmartScreen-Filter-frequently-asked-questions-IE9?SignedIn=1)
“It doesn't necessarily mean the website is fraudulent or that the program is malware, but you probably shouldn't download or install the program unless you trust the website and the publisher.”

The Windows operating system has also increased the warnings, and has made it more of a hassle to install many programs (not just ours).

All of our installation files are constantly being checked for viruses and malware by independent organisations.
Please go to our Awards and Verification page for a list of some of the companies that do these checks.

There will be a way to continue installing the software, the method depends on the version of Windows or Internet Explorer you are using.